Red dendrocronológica del pino de altura (Pinus hartwegii Lindl.) para estudios dendroclimáticos en el noreste y centro de México

Properties of the subduction system in Mexico

Palaeolimnological records of climate change in México — Frustrating past, promising future?

Honey bees (Apis mellifera L.) play an important ecological and economical role. Recently, Europe and the US have reported an increase in honey bee colony losses owing to several factors. Several possible causes for colony losses have been proposed, including exposure to pesticides such as agrochemicals for crop protection and pesticides for veterinarian use inside the hive. Mexico lacks reports about pesticide residues in hive products (honey, beeswax, pollen, propolis and royal jelly). This study presents the analysis of 93 agricultural pesticide residues found in honey and beeswax samples from Yucatan, the main area of beekeeping in Mexico, and from hives in Northeastern and Central Mexico, as well as in commercial wax samples. The number and concentrations of pesticides found are dependent of region. Yucatan hive samples had the lowest levels of agrochemicals. In Yucatan, the main agrochemical found in honey was the fungicide phenylphenol, while in wax combs, the agrochemicals found in the highest concentrations were the phenylphenol and the organochlorine 2,4′-DDT. In Northeastern Mexico, the main pesticides detected in wax and/or honey were malathion, chlorpyrifos, phenylphenol and thiabendazole, whereas in Central Mexico, the most common residues were chlorpyrifos and imidacloprid. Commercial wax showed low levels of pesticides residues. Malathion concentration in one sample of honey taken from Northeastern Mexico exceeded the European Maximum Residue Levels (MRL = 0.05 mg/kg).

Radiogenic strontium isotopes (87Sr/86Sr) have long been used in analyses of paleomobility within Mesoamerica. While considerable effort has been expended developing 87Sr/86Sr baseline values across the Maya region, work in central Mexico is primarily focused on the Classic period urban center of Teotihuacan. This study adds to this important dataset by presenting bioavailable 87Sr/86Sr values across central Mexico focusing on the Basin of Mexico. This study therefore serves to expand the utility of strontium isotopes across a wider geographic region. A total of 63 plant and water samples were collected from 13 central Mexican sites and analyzed for 87Sr/86Sr on a Thermo-Finnigan Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). These data were analyzed alongside 16 published 87Sr/86Sr values from two additional sites within the region of interest. A five-cluster k-means model was then generated to determine which regions of the Basin of Mexico and greater central Mexico can and cannot be distinguished isotopically using 87Sr/86Sr values. Although the two clusters falling within the Basin of Mexico overlap in their local 87Sr/86Sr ranges, many locations within the Basin are distinguishable using 87Sr/86Sr values at the site-level. This study contributes to paleomobility studies within central Mexico by expanding knowledge of strontium isotope variability within the region, ultimately allowing researchers to detect intra-regional residential mobility and gain a greater understanding of the sociopolitical interactions between the Basin of Mexico and supporting outlying regions of central Mexico.

Radiogenic strontium isotopes (87Sr/86Sr) have long been used in analyses of paleomobility within Mesoamerica. While considerable effort has been expended developing 87Sr/86Sr baseline values across the Maya region, work in central Mexico is primarily focused on the Classic period urban center of Teotihuacan. This study adds to this important dataset by presenting bioavailable 87Sr/86Sr values across central Mexico focusing on the Basin of Mexico. This study therefore serves to expand the utility of strontium isotopes across a wider geographic region. A total of 63 plant and water samples were collected from 13 central Mexican sites and analyzed for 87Sr/86Sr on a Thermo-Finnigan Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS). These data were analyzed alongside 16 published 87Sr/86Sr values from two additional sites within the region of interest. A five-cluster k-means model was then generated to determine which regions of the Basin of Mexico and greater central Mexico can and cannot be distinguished isotopically using 87Sr/86Sr values. Although the two clusters falling within the Basin of Mexico overlap in their local 87Sr/86Sr ranges, many locations within the Basin are distinguishable using 87Sr/86Sr values at the site-level. This study contributes to paleomobility studies within central Mexico by expanding knowledge of strontium isotope variability within the region, ultimately allowing researchers to detect intra-regional residential mobility and gain a greater understanding of the sociopolitical interactions between the Basin of Mexico and supporting outlying regions of central Mexico.

There is a growing number of studies that use historical sources to reconstruct recent environmental change. In Mexico there are abundant sources of information that can be used to determine variations in the climate over the historical period. In this paper we draw together information from a variety of primary and secondary historical sources to reconstruct fluctuations in the climate of central Mexico over the last 600 years. The Aztecs are believed to have entered the Basin of Mexico during a period of severe drought. Wet conditions, however, characterized much of the Aztec (AD 1345-1521) and early colonial period prior to a return to drier conditions in the 1640s. Between 1640 and 1915, a series of severe droughts caused widespread devastation throughout central Mexico, particularly during the mid- to late 1700s and late 1800s. Since the early 1900s this region has experienced slightly wetter conditions. The climatic record from the Basin of Mexico is compared with proxy climatic data from two other areas in Mexico: a detailed lake-level curve from Lake Patzcuaro in central Mexico and the few tree-ring records from northern Mexico. Although the palaeoclimatic records from central Mexico are similar, there is greater divergence between the records from central and northern Mexico. In general, fluctuations in the climate over the last 600 years can be explained by changes in the relative strength of the summer 'monsoon', but it is possible that ENSO events can cause considerable differences in prevailing climate conditions in the northern and central parts of the country.

SUMMARY Prediction of ground motion in central Mexico is of great consequence not only for Mexico City but also for several other cities in the region. However, the geometry and velocity distribution of the geological structures in central Mexico is unknown. In this paper, the velocity structure in central Mexico is investigated using seismic noise records from three different arrays, one permanent and two temporary. Distances between stations span 3–300 km. Seismic noise is analysed using time domain cross-correlation to estimate the Green's function between stations. Only the fundamental mode of Rayleigh waves is recovered in the cross-correlation of vertical component records, between 5 and 10 s period. At smaller periods, we obtain no correlation, even between closely spaced stations. This suggests that the heterogeneity of the Trans-Mexican Volcanic Belt (TMVB) hampers the propagation of Rayleigh waves smaller than 9 km. We observe a large velocity contrast between the Guerrero terrain and the TMVB. This velocity contrast, measured here for the first time at this scale, explains the appearance of regional amplification in central Mexico and the origin of the diffracted waves behind the long duration of ground motion observed in Mexico City. In the large scale, average Rayleigh wave group velocity at 5 s period is about 2.5 km s−1 in the TMVB and larger than 3.6 km s−1 outside it. Significant lateral heterogeneity is evident. In the stations of the dense Meso-American Subduction Experiment array we analysed, we observe in addition a significant increase in velocity from north to south in the central portion of the TMVB. Our results are part of ongoing studies with the final objective of building a model of TMVB that may be used to simulate ground motion in central Mexico from subduction zone earthquakes.

Distribution of hydrous minerals in the subduction system beneath Mexico

A hypothesis of historical area relationships for Mexico, Central, and South America was investigated by a cladistic biogographic analysis using 10 taxon cladograms of the herpetofauna of Mexico. A hypothesis is presented based on previous narrative biogeographic scenarios and compared with the general area cladograms (GACs) obtained using reconciled trees of COMPONENT 2.0 and Brooks Parsimony Analysis (BPA). For tree reconciliation, 1 000 trees were saved after the analysis. BPA yielded 18 GACs (CI = 0.805, RI= 0.549). The GAC derived from tree reconciliation is more or less pectinate and has only 3 groups of 2 areas each. These groups consist of the Chihuahuan and Sonoran deserts as sister areas on the one hand (DCHI, DSON), and the Sierra Madre Oriental and Occidental as sister areas on the other (SMOR, SMOC). This latter clade is sister to the Chihuahuan and Sonoran desert clade. The third group has the Transvolcanic Belt and Sierra Madre del Sur as sister areas (TVA, SMEX). The GAC obtained by BPA showed 4 main groups of areas: the fi rst is comprised of the Pacifi c coast of Mexico and the Balsas Depression (PCBAL), the Sierra Madre del Sur (SMEX), and the Transvolcanic Belt (TVA); the second group includes the Sierra Madre Oriental (SMOR), Sierra Madre Occidental (SMOC), Sonoran (DSON) and Chihuahuan deserts (DCHI); the third comprised the Highlands of Chiapas and Guatemala (CHIG), the Eastern Lowlands, on the Atlantic coast (ELL) and the Semiarid Lands of Tamaulipas-Texas (TAMS); the fourth group contains the Western Lowlands, in the Pacifi c coast (WLL) and northern South America (SA); the Talamanca Ridge (TALA) is isolated at the base of the 3 fi rst groups. The GAC from narrative biogeography contains 3 groups: the fi rst has areas of northern Mexico (DSON, DCHI, TAMPS), the second has areas from central Mexico (PCBAL, SMOR, SMOC, TVA), and third has areas from southern Mexico and Central America (SMEX, CHIG, TALA, WLL, ELL, SA). In general, the GAC from the BPA analysis shared more groups with the hypothesis of narrative biogeography; when compared to the GAC obtained via reconciled trees; however, all the GACs obtained are topologically distinct. Accounting for the lack of congruence between the narrative biogeography GAC, reconciled tree analysis and BPA, is challenging due to several factors: 1), erroneous interpretation of vicariant events when constructing the narrative area cladogram; 2), lack of congruence among patterns of speciation and endemism for the taxa used in this analysis; 3), the region under study is a geologically complex zone and the history of the inhabiting biota is equally complex; 4), there are many widespread species present in this region, and may obscure the relationship among the areas of endemism; 5), the patterns of endemicity are poorly-defi ned and -studied in Mexico and Central America; 6), the incorrect selection of the areas of endemism used in this study. Despite these issues the results presented here are evidence of the multi-dimensional complexity of historical biogeographical processes in the region.

Tree rings as indicators of climatic variation in the Trans-Mexican Volcanic Belt, central Mexico

Arceuthobium vaginatum (Willd.) Presl subsp. vaginatum (family Viscaceae) is the most widespread and common dwarf mistletoe in Mexico (2). Although most dwarf mistletoes are considered to be relatively host-specific parasites, this species has the broadest host range found in the genus. It has been reported to infect 13 species of pines (Pinus spp., family Pinaceae) (2). Pinus pseudostrobus Lindl. is a common pine within the geographic range of A. vaginatum and has been reported as possibly being immune to this mistletoe (2). However, we have found a location in the Sierra Madre Oriental, Nuevo Leon, Mexico where A. vaginatum subsp. vaginatum is severely parasitizing P. pseudostrobus. The stand of infected P. pseudostrobus is located approximately 3 km east of Laguna de Sanchez(25°19'42″N, 100°15'45″W, elevation 1,950 m). Several hundred P. pseudostrobus are infected at this location; several trees in the stand have one or more dwarf mistletoe infections on nearly every branch and many trees have bole infections. P. pseudostrobus is the only pine growing at this locality, and the extent of infection on this pine clearly indicates it is highly susceptible to A. vaginatum subsp. vaginatum. Hawksworth and Wiens (2) based their tentative classification of P. pseudostrobus as immune to A. vaginatum subsp. vaginatum on observations of uninfected P. pseudostrobus growing near severely infected pines in central Mexico. The discrepancy between the susceptibility of P. pseudostrobus in central Mexico and in Nuevo Leon may be related to the different taxonomic classifications afforded these populations by different pine taxonomists. For example, Perry (3) considers the populations of P. pseudostrobus growing in Nuevo Leon to represent P. pseudostrobus forma megacarpa Loock, while Farjon and Styles (1) treat these populations as typical P. pseudostrobus. Whether the high level of susceptibility of the P. pseudostrobus population near Laguna de Sanchez indicates these populations are taxonomically distinct from typical P. pseudostrobus needs further study, but the severe infection we observed in Nuevo Leon clearly demonstrates that P. pseudostrobus should be reclassified as a principal host of A. vaginatum subsp. vaginatum in northeastern Mexico. Specimens of A. vaginatum subsp. vaginatum on P. pseudostrobus have been deposited at the Deaver Herbarium, Northern Arizona University, Flagstaff (Accession No. 76455). To our knowledge, this is the first report of A. vaginatum subsp. vaginatum on P. pseudostrobus. It should also be noted that the population of A. vaginatum subsp. vaginatum near Laguna de Sanchez is 150 m below the lower elevation limit previously reported for this dwarf mistletoe in Mexico (2).

AimOur aims were to determine the pattern of genetic variation in the endemic shrub Nolina parviflora, and to evaluate the influence of the geological history of the Trans‐Mexican Volcanic Belt (TMVB) and nearby mountainous regions on plant population divergence.LocationTrans‐Mexican Volcanic Belt, Sierra Madre Occidental, Sierra Madre Oriental and Sierra Madre del Sur mountain ranges in Mexico.MethodsTwenty‐eight populations (210 individuals) were sequenced for one nuclear (rpb2) and two chloroplast (trnL–F and psbA–trnH) DNA markers. Intraspecific phylogenetic relationships among haplotypes were reconstructed, and molecular dating, population genetic analyses and group testing were performed on the data. Isolation‐by‐distance analysis was conducted for the populations spanning the distribution of the species.ResultsTwenty‐four chloroplast marker haplotypes and 36 rpb2 haplotypes were recovered from the populations sampled. The combined marker phylogeny indicates the presence of two well‐supported clades within the N. parviflora populations. Clade 1 includes populations from Jalisco and Zacatecas and Clade 2 comprises the remaining populations. We found an east–west geographical pattern of chloroplast DNA (cpDNA) haplotype distribution, indicating a lack of gene flow between these two regions. Divergence time estimates indicate an Oligocene to mid‐Miocene divergence between Nolina and Dasylirion. Divergence estimates for Clade 1 are from the mid‐Miocene to early Pleistocene, and for Clade 2 from the early Miocene to mid‐Pliocene. Values of cpDNA GST (0.702) indicate a strong population structure and differentiation. A spatial analysis of molecular variance indicates 11 groups among the sampled populations and detects various well‐supported geographical barriers.Main conclusionsDivergence time estimates suggest a correlation between the time of divergence between distinct N. parviflora populations and periods of uplift in the TMVB. We infer that the orogeny of this mountain range played an important role in driving the diversification of plant populations in central Mexico by creating topographical barriers that limited gene flow.

Constructing Identity: The Role of Food in Mexica Migration and Creation Accounts

Petrographic and detrital zircon U-Pb analysis of modern beach sands and river sands from major catchments in northeastern Mexico draining to the Gulf of Mexico provides evidence for a minimum of 650 km of littoral sand transport southward from the mouth of the Rio Grande at the Mexico-U.S. border to the central part of the state of Veracruz, Mexico. Principal tracers of Rio Grande sand include: (1) quartzose composition that contrasts with lithic compositions of sand in eastern Mexico rivers and (2) detrital zircon ages with Mesoproterozoic modes at 1.8−1.5 Ga and 1.4 Ga, age groups that are typical of basement and derivative sediment of the SW United States but are uncommon to rare in Mexican river catchments. In contrast, abundant Miocene and younger grains in beach sands of Veracruz indicate primary sediment derivation from active and recently active volcanoes in the Trans-Mexican volcanic belt in central Mexico. A proportional decrease in sand of Rocky Mountain provenance with distance southward along the coast from the mouth of the Rio Grande and absence of Miocene and younger zircon grains in beaches north of rivers draining the Trans-Mexican volcanic belt indicate net littoral sand transport southward along the eastern coast of Mexico, demonstrating that wintertime shoreline-parallel surface currents rather than north-directed summertime currents dominate sediment transfer. Sand samples of Tamaulipas beaches in northeastern Mexico commonly have equal or higher proportions of U.S.-derived Mesoproterozoic zircon grains than are present in river bar sand of the lower Rio Grande and the Rio Grande delta, and thus require that littoral processes rework and incorporate coastal dune and beach sands of northeastern Mexico that are enriched in predam Rio Grande sediment. Implied coastal erosion may be related to Holocene transgression or interruption of sediment supply to the coastal sediment transport system by dams in the Rio Grande drainage basin. Such coastal erosion is impacting long-term shoreline stability and viability of the littoral environment.

Identification of recharge processes and mixing patterns by using CFC's and isotopic multi-tracing (δ18O, δ2H) of groundwater in a stratified volcanoclastic aquifer of the semiarid Amazcala Basin in Central Mexico